Common Vision Problems
Sharp, clear vision is the result of light rays passing through the cornea, pupil and lens of the eye and focusing directly on the retina. If the cornea is not round, or is too steep or too flat in relation to the length of the eye, light rays focus either in front of or behind the retina. This results in _refractive errors_ such as nearsightedness, farsightedness, and astigmatism. Laser vision correction improves the way the eye focuses light by modifying the curvature of the cornea and re-focusing the light directly on the retina.
Nearsightedness, or myopia, occurs when the curvature of the cornea is too steep or the eyeball is too long. With nearsightedness, the eye's strong refractive power forces the image to be focused in front of the retina, rather than on it. When light focuses in front of the retina, near objects can be seen clearly, but far objects appear blurry. Myopia can be treated by flattening the cornea with LASIK, PRK, or LASEK. An alternative non-laser procedure, Implantable contact lens (ICL) eye surgery, can correct myopia by implanting a special type of lens inside the eye.
Farsightedness, or hyperopia, is caused when the curvature of the cornea is too flat, or the eyeball is too short, forcing light to focus behind the retina. With farsightedness, the eye's weak refractive power causes far objects to be seen more clearly and near objects to appear blurred. The eyes may have to strain to maintain things in focus. The first appearance of hyperopia is strongly age-dependent; younger patients have much less difficulty with hyperopia. Hyperopia can be corrected by steepening the central cornea with LASIK, PRK or LASEK or CK.
Astigmatism occurs when the cornea is irregularly shaped - like a football or a teaspoon - preventing light from converging on the retina. Parts of the image may focus on the retina, while others focus behind it or in front of it. This has the effect of bending light inconsistently and causing blurred or distorted images. Astigmatism can occur alone or in addition to either nearsightedness or farsightedness. Although astigmatism can complicate refractive surgery, it can be effectively corrected with LASIK, PRK or LASEK.
Several types of visual imperfections, referred to as lower- and higher-order aberrations, can exist within the same eye and affect both visual acuity and the quality of vision. Lower-order aberrations, like nearsightedness, farsightedness, and astigmatism, contribute to approximately 80% of refractive errors. They affect how much you see. Higher-order aberrations account for the remaining 20% of error and affect how well you see. They can be compared to smudges or spots on your glasses and have been linked to halos and glare that cause vision problems at night. Higher-order aberrations have not been treatable by conventional laser vision correction procedures. Now, Wavefront technology and Custom LASIK can quantify and correct these higher-order aberrations.
Presbyopia is a condition that occurs as you age. The lens in your eye loses its elasticity and is no longer able to focus on images up close. Most people over the age of 40 and everyone over the age of 50 will become presbyopic and experience difficulty reading the fine print of a menu or a phonebook. In the past, presbyopia was corrected with the use of reading glasses. Now there are non-laser vision correction procedures that can postpone the effects of presbyopia.
A cataract is formed when the natural lens of the eye hardens and becomes cloudy, resulting in a loss of visual function. Cataracts are a normal part of aging and about 50% of all Americans over 65 have cataracts, as do 70% of those aged 75 and over. Cataracts can affect all ages, however, as they also result from injury, heredity, or certain medications.
A cataract is painless and usually develops gradually over several months or years. The beginning of a cataract in one or both eyes may cause decreased night vision, impaired depth perception, and increased color distortion. There is no single, objective test for cataracts. A doctor analyzes patient symptoms, performs a regular eye exam, and may test for glare disability and contrast sensitivity to make a diagnosis.
A stronger eyeglass prescription may help improve vision or be treatment enough. Just because you have a cataract doesn't mean it must be removed immediately; cataract surgery can almost always be postponed until you are unhappy with the way you see. If you do have surgery, it is performed under local anesthesia on an outpatient basis. The clouded lens is fragmented using a high frequency ultrasound probe and then removed. In either case, an artificial lens is then implanted to take the place of the lens that was removed. It takes a few weeks for the eye to heal completely, but the patient is able to return to normal activity soon after surgery.
Cataract surgery has an overall success rate of 98 percent. It has provided improved quality of life for millions of Americans by increasing their independence through improved vision.
Here are some links to site with further information on eye and vision problems: